The separation of solids from another wherein one solid is separated by floating at or near the surface of a fluid, i.e. flotation unit operation has and is employed in a plethora of industries. Originally developed for mineral concentration, flotation techniques have been extended into other fields, e.g. the separation of hulls from wheat kernels, printer's ink from the newspaper pulp, potassium chloride from sodium chloride, etc.
Various assemblies and devices have been used in the formation of microbubbles. Early efforts have been directed to the use of orificed conduits disposed in the lower portion of a tank and into which pressurized air is introduced to form streams of microbubbles in the material being treated such as illustrated in U.S. Pat. No. 3,161,590 to Weis, et al. Alternately, adjustable diffusser and injection assemblies, such as disclosed in U.S. Pat. No. 1,922,920 to Aherne wherein a water and gas stream are contacted and admixed for introduction into a flotation tank.
The use of turbulent flow principles for injecting microbubbles into a sewage effluent using Venturi principles is disclosed in U.S. Pat. No. 4,019,983 to Mandt. Such assemblies and devices are generally designed without liquid flow considerations but primarily bubble formation, and thus not with reference to bubbles per unit volume of liquid. Additionally, microbubble production by pressurization requires large eguipment including pump, tank, pressure relief valves and supporting equipment.